Various actuator and lifter devices with rack and pinion gearing have been previously used for many different applications, including conveying and transferring workpieces, lifting formed sheet metal parts from stamping dies, and the like. In many applications, it is necessary that the actuator device be compact and small relative to its load bearing capabilities.
One such compact lifting device with an actuator rack driven by a pinion gear is shown in U.S. Pat. No. 3,400,593. A plurality of these devices may be linked together to drive their respective racks in unison by a non-circular connecting shaft removably engagable with the pinion gear for rotation in unison therewith. This arrangement also enables the racks to be positioned at a desired location with respect to a common reference plane before the devices are operably linked together by the non-circular connecting shaft. If desired, a single device can have a plurality of racks each with an associated separate pinion with all of the pinions of the device being operably coupled together by a non-circular shaft so that the racks will be driven in unison.
With this compact lifting device, problems have been experienced with the durability, strength and load bearing capacity or capability of the bearings and pinion gears, and particularly with pinion gears having a pitch diameter of less than about two inches. In use, these pinion gears are susceptible to permanent deformation, distortion, cracking, and fracturing, have a relatively short useful life and require considerable service, maintenance and replacement. Moreover, when they fail they frequently damage other components of the device which also then require replacement or scrapping of the entire device.
Moreover, problems have been experienced with the lubrication, durability and wearability of the bearings for the rack which frequently resulted in bearing failure after only a few thousand cycles of the lifting device.